There are many different methods for gene delivery, including the use of DNA, RNA or viral vectors. Viral vectors are widely used to date because when introduced into host cells by viral vectors, genes can be stably expressed for a long period of time in the host cells (Cancer Gene Ther. 1994; 1:51-64). Of the viruses used for mediating gene delivery, however, retroviruses and lentiviruses have problems in clinical application because they may cause the gene of interest to be incorporated into the chromosome of the host cells, which may result in a mutation. In contrast, when adenoviruses are manipulated so as not to be incorporated into the chromosome of the host cell, the recombinant adenoviruses may be free from association with oncogenesis and thus be safe. In addition, E1/E3-deleted recombinant adenovirus is more safe because it is not only replication deficient due to E1 deletion, but also does not alter the immune response of the host cells due to E3 deletion. In addition, an adenovirus has additional advantages making it suitable for use as a vector (Curr Opin Genet Dev. 1993; 3:499-503). That is, an adenovirus can accommodate a gene insert as large as up to 8 kb and express it at a high concentration. Moreover, adenovirus can infect many different cells. Although epithelial cells of the eye, the respiratory tract, the intestine and the urinary tract are the most susceptible to adenoviral infection, an adenovirus can infect the liver, the muscles and the heart of mice as well as nerve cells, hepatic cells, lymphocytes, macrophages, endothelial cells, and fibrocytes.
However, because the intracellular uptake of the adenovirus particle is primarily mediated by the coxsackievirus and adenovirus receptor (CAR), it is very difficult to apply an adenovirus to the effective introduction of genes into cells that have a low level of CAR, such as cancer cells and stem cells (J Clin Invest. 1997; 100: 2218-2226.). One strategy for overcoming this problem is to employ a genetically modified recombinant adenovirus that has an increased MOI (multiplicity of infection) or which can infect cells independently of the receptor. In addition to the genetic manipulation of the adenovirus itself, an external factor, such as a liposome, a cation, a cytopermeable peptide, etc. may be used to form a complex with recombinant adenovirus which can invade irrespective of the expression of CAR.
A great barrier to the gene therapy based on a recombinant adenovirus is a neutralizing antibody (nAb) to adenovirus. Adenoviral infections frequently occur in people, generally without causing serious symptoms. Thus, immune responses to adenoviruses are induced in most people so that they have neutralizing antibodies to adenoviruses. Due to this, recombinant adenoviruses, when injected to deliver a gene, cannot enter target cells, but are removed by neutralization (Clin Diagn Lab Immunol. 2004; 11:351-357). Therefore, a strategy for evading the attack of neutralizing antibodies is required for the application of vaccines and gene therapeutics based on recombinant adenoviruses to have practical use. According to reports to date, encapsulation of adenoviruses with liposomes using lipids such as cholesterols or with (polyethylene glycol) or PLGA (poly lactic-co glycolic acid) makes it possible to avoid the attacks of neutralizing antibodies to some degree (Mol. Ther. 2002; 5:233-241, Gene Ther. 2005; 12:579-587, Gene Ther. 1998; 5:740-746.). However, such single materials cannot encapsulate the whole adenovirus completely, so that infectivity is still decreased by a high concentration of neutralizing antibodies. What is more important, the encapsulation may mask ligands for the adenovirus receptors, resulting in a decrease in the uptake of the virus by the cells that express CAR as well as by the cells that do not express CAR. Therefore, there is a pressing need for the development of a novel adenovirus composite that can compensate for the drawbacks of the encapsulation.
As reported previously, cations such as calcium (Ca2+) mitigate electrostatic repulsion between adenoviral capsids and cellular membranes, both being negatively charged, and combine with phosphates to form co-precipitates with adenoviruses, allowing the virus particles to mediate CAR-independent gene delivery (J Clin Invest. 1998; 102:184-193.). In addition, a recent study has reported that the lanthanide elements including lanthanum (Lantanium, (La3+) and gadolinium (Gd3+), which are trivalent cations, have relatively stronger positive charges per volume and are more effective in mitigating electrostatic repulsion, compared to a calcium ion, which is a divalent anion (Gene Ther. 2008; 15:357-363). However, upon intracellular uptake, the lanthanide elements, which are non-dietary minerals, have the likelihood of interfering with main metabolic reactions such as enzymatic actions or neurotransmission. Hence, it is reluctant and difficult to apply the lanthanide elements to clinical practice.
Iron (Fe) is a transition element with the atomic number 26, which can be a di- or trivalent cation. In the body, iron plays an important role, acting as a main component of hemoglobin, which is responsible for oxygen and carbon dioxide transport. Thus, the biological function of iron is responsible for providing energy to power the functions of the organism. In addition, iron is highly biocompatible with and safe to the body, as proven by its abundance in the body. The iron precipitate ferric phosphate is also not toxic to the body.
However, little study has been done on the use of iron ions in the delivery of viral vectors into cancer cells and stem cells that do not express CAR.
Thus, a novel viral composite that can introduce a viral vector independently of CAR expression and can effectively evade anti-viral neutralizing antibodies is needed.